Weight isn't the sole determinant of lock quality. The lock I use is relatively light compared to some that have been mentioned.

Force 3 ( http://www.amazon.com/Master-Lock-81.../dp/B00194D594 ). It weighs 1kg and has a "Gold" rating from the Master Locksmith's Association.

By contrast, the Kryptonite Evolution Mini and Mini LS mentioned above weight the same as mine but only earn a "Silver" rating.